Currently, a flat display structure is generally adopted in a display unit used for displaying words, images, videos, and interaction interfaces. In this field, for example, an electro fluidic display system (Electro fluidic display system, EFD), an electrophoretic display system (Electrophoretic display system), in-plane-switching (In-Plane-Switching, IPS), an electro-osmosis display system (Electro-osmosis display system), and liquid crystal display LCD, are widely used. A part of the display structures thereinto use a reflection-type display, such as the EFD applied to electronic ink (E ink) or electronic paper. The EFD may also be called electrowetting display (Electrowetting display), and the electrowetting refers to changing the wettability of a droplet on a substrate through changing the voltage between the droplet and an insulating substrate, i.e., changing a contact angle to make the droplet be deformed and displaced. The so-called wetting refers to a process that a liquid on a solid surface is replaced by another liquid. The liquid can be spread on the solid surface, and the contact surface between the solid and the liquid tends to be expanded. That is, the adhesive power of the liquid to the solid surface is greater than the cohesive force thereof, which is wetting namely. The liquid cannot be spread on the solid surface, and the contact surface tends to be shrunk into a spherical shape, which is non-wetting namely. The non-wetting is just that the adhesive power of the liquid to the solid surface is less than the cohesive force thereof, wherein the wetting effect of a hydrophobic surface may be changed by voltage (thus named electrowetting), which enables the surface to become more hydrophilic (wetting). Because the original hydrophobic surface becomes more hydrophilic currently, the original inert liquid that is well contacted with the hydrophobic surface, such as an oil layer, has to be changed in form. This interface property control is the basis of applying the electrowetting. The application of an electrowetting display principle has been described in details in the patent application, WO03071347 and the contents published in 425383385 of the publication “Nature”, which are both incorporated herein by reference.
The principle structural drawings of an EFD pixel unit structure are as shown in FIG. 1a and FIG. 1b, and a pixel wall 3 is arranged above a dielectric layer and a photoetched lower electrode 5. An insulating layer in the top layer has hydrophoby, and is thus called as a hydrophobic insulating layer 6. A first liquid 1 (such as an oil layer) has good wettability in the hydrophobic insulating layer 6, and is thus used for filling an area limited by the pixel wall 3. A second liquid 2 and the hydrophobic insulating layer 6 are not wetted, and the second liquid is incompatible with the oil layer, and fills the top of the unit structure.
When a voltage is applied to the electrode, an electric charge is accumulated in the lower surface of the second liquid 2, and then overcomes a capacitance power to puncture the oil layer. The oil layer punctured may be pushed to a corner of a pixel area through further increasing the voltage. If the voltage is eliminated, the oil compressed will return to a state before applying the voltage. As shown in FIG. 1a, the oil layer is filled in the area 1 as shown in the figure before applying the voltage; and as shown in FIG. 1b, the oil layer is pushed to one side of the pixel unit structure after applying the voltage. If proper pigment is added in the oil layer, such as black pigment, the pixel shows lightproof black while overlooking the pixel unit from the position of FIG. 1a. while the pixel is light-transmitting at the position of FIG. 1b. In case of a reflective display, the color of a reflecting layer below the pixel is presented as, for example, white.
In order to puncture the oil layer, a proper charge intensity needs to be used, which is defined as follows.
  ρ  =      ɛ    ⁢          V      d      wherein, V is the voltage applied, ∈ is a dielectric constant, and d is thickness. Due to technical effects, such as the thickness change of the dielectric layer and the filling nonuniformity of the oil layer, the charge intensity on the surface of the oil layer may be different, which will cause the following problems.
1) The puncture points of the oil layers having different pixels may be different; and
2) The movement of the oil layer punctured in this way cannot be predicted.
The problems above will bring defects during the working time of the EFD apparatus, which is not expected to be seen by a user.
In addition, the existing pixel design has a severe problem of hysteresis effect, which is as shown in FIG. 2. A horizontal axis refers to the voltage V applied, while a vertical axis refers to the pixel area opened. The voltage applied is increased from a zero point O to a threshold voltage Vth (threshold point A in FIG. 2), so that the oil layer is punctured by the second liquid 2. After the oil layer is punctured, the shrinking of the oil in the pixel is very sensitive to the voltage applied, which makes it very difficult to modulate the area opened. When the voltage applied exceeds a certain numerical value, the area opened becomes saturated (a saturation point B in FIG. 2). If the voltage applied is decreased, then the opened area of the pixel is decreased following different routes (as a cutoff route BCO shown in FIG. 2), which is the so-called hysteresis effect. However, a smaller hysteresis effect in the EFD display apparatus is usually expected, so that a pixel gray scale (which is corresponding to the size of the opened area of the pixel in proportion) may be easily modulated through applying the voltage.